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Paul Ehrlich has predicted that we humans will turn to cannibalism in the not too distant future as the only way to stop ourselves being hungry. I would take this as evidence that Paul Ehrlich has finally and irretrievably lost the plot. He's been known for 50 years now as one of the great voices crying in the wilderness about the perils of overpopulation. The problem is that absolutely none of his predictions have come to pass. And the reason for that is that he's reasoning from the wrong evidence base. He is, by original training, an entomologist: someone who studies insects. And human beings are not insects: we have agency for a start, as well as intelligence. A far better predictor of what is, has and will, happen about human population can be found in the work of Gary Becker, the economist, than in Ehrlich, the entomologist. The reason being that economists do attempt to explain how humans act in contrast to the entomologists who are trying to describe how insects act.

The comments about cannibalism came at HuffPo Live. A partial transcript is here.

Host John Zepps asked Ehrlich if in the decades and centuries to come, we will need to change the way we use and consume animals. Not to worry, Ehrlich said.

“I don’t think there’s going to be the centuries to come with our kind of civilizations and with the kind of ethical issues that at least some people (Republicans) in our civilization are concerned with,” he said, chuckling. “I think the issues are more likely to be “is it perfectly OK to eat the bodies of your dead because we’re all so hungry.”

There's one obvious problem with this: which is that a human being's cadaver would feed another human being for about a month, tops. So there's not actually enough dead bodies around, nor can there be, to support any significant number of people. It might sound rather callous to point this out but human beings are simply too slow growing to become a reasonable food source for other human beings. We need something that's rather faster to put on weight than ourselves.

But that trivia aside the mistake that Ehrlich is making is to think that we humans do in fact breed like insects. Or as the Reverend Malthus thought we did. Which is to say that when the food supply increases then more people survive. Thus we always expand the population to the limits of the possible food supply. Given that Ehrlich thinks that the methods we use to expand this supply (fertilisers, irrigation, industrialised farming) cannot be maintained for very long therefore there's going to be starvation and a mass population crash. But this isn't actually the way that human beings work.

As Gary Becker pointed out in his economic study of the family as our income (or wealth, choose whichever you prefer) rises then we tend to have fewer children, not more. And this has been happening in every single human society as it gets richer. So much so that we expect to see the peak of human population in about 30 years' time. For we expect just about everywhere to go through that wealth (or income) level where fertility declines in the next few years. So much so that even the UN, not normally all that up to date on these sorts of things, is predicting that human population in 2100 will be lower than it will be in 2050, or even than it is today. And historically the UN has rather overestimated population numbers.

What further damages Ehrlich's case is that the shortages of all of those things that make up industrialised farming aren't about to happen either. Even climate change is expected to increase agricultural yields up to about 2080.

Ehrlich's predictions have always been a little wild, not one of them has ever actually come true, but this idea that we're imminently about to start eating the dead is proof of little more than that he's ever further from the plot, irretrievably lost in the nonsense of his own misunderstandings of the world around him.